1. Field of the Disclosure
This specification relates to an enhancement-type nitride semiconductor device having a passivation layer formed using a photoelectrochemical (PEC) method, and a fabricating method thereof.
2. Background of the Disclosure
A nitride semiconductor exhibits several advantages including high threshold electric field, low On-resistance, high temperature, and high frequency applications. The spotlight to the nitride semiconductor comes from those advantages, and advanced researches on the nitride semiconductor as a material for the next generation semiconductor device are conducted.
In recent time, mainstream high power devices include MOSFET and IGBT, and also devices such as GaN-based HEMT, HFET, MOSFET and the like are studied.
The HEMT which uses high electron mobility is employed for communication devices exhibiting high frequency performance.
Also, the HEMT is used in power semiconductors, communication devices showing high frequency performance, and the like. In recent time, developments of hybrid/fuel cell cars are ongoing, and various overseas corporations are releasing hybrid vehicles. Reliable operations at high temperature are required for semiconductor switches, which are disposed within voltage booster converter and inverter for connecting a motor to a generator within a hybrid vehicle, due to heat generated from an engine. Gallium nitride (GaN) may allow for the reliable operations at the high temperature owing to its wide bandgap, so as to be proper as the next generation semiconductor switch within hybrid cars.
Among others, Furukawa Electrics in Japan has issued an AlGaN/GaN high-electron-mobility transistor (HEMT) discrete, which has a high breakdown voltage of 750V and a low On-resistance of 6.3 mΩ-cm2. It has thusly been proved that the HEMT has superior characteristics to the conventional Si MOSFET, Si superjunction MOSFET and SiC MOSFET. Also, the issued GaN discrete has shown a stable switching operation at a high temperature of 225.
FIG. 1 is an exemplary view showing a general structure of Heterojunction Field Effect Transistor (HFET).
As shown in FIG. 1, a general HFET 10 may switch a 2 DEG current, which flows from a drain electrode to a source electrode, through a schottky gate electrode.
The general HFET 10 may include a substrate (not illustrated), a first GaN layer 11 formed on the substrate, an AlGaN layer 12 on the first GaN layer 11, a second GaN layer 13 on the AlGaN layer 12, and a gate electrode 14, a source electrode 15 and a drain electrode 16 all formed on the second GaN layer 13.
Many attempts have been made to use this type of HFET device as a high-output power device, by virtue of excellent voltage and current characteristics of the HFET device. However, the HFET device may have a disadvantage in that it is a normally-on type device, unlike other devices such as MOSFET, IGBT and the like.
Since the normally-on device is difficult to be produced due to high complexity in constructing a circuit, several methods, such as plasma processing, p-GaN growth, gate recess and the like, are on the course of the studies, as a way for increasing a threshold voltage.